Large gear cutting machines are known from the prior art which can currently machine machining diameters of 16,000 mm and more. In this respect they are hobbing and profile milling machines as well as gear planing machines. These machines are also available as gear grinding machines and gear shaping machines for somewhat smaller workpiece diameters.
Since the workpieces for the gear cutting process come from a preprocessing such as a forging operation or are assembled from individual segments with very large workpieces, they first have to be subjected to a turning, milling and/or drill machining before a gear cutting machining in order thus to provide the functional surfaces for the use of these gears. The throughput times for these machining operations can take one day up to several days in part, including the set-up times, with workpieces of this order of magnitude.
The usual separation of premachining operations and gear cutting operations onto a plurality of individual machines customary in mass production represents a substantial investment cost in a plurality of machines on the manufacture of large teeth and then also has the consequence of a large space requirement for the setting up of the individual machines. Complete production halls then fast become planned for such machines. Machines of this dimension also usually require a huge additional foundation so that these machines cannot be repositioned in the production area without problem. Substantial investment sums result from this which only pay their way when corresponding volumes are also provided.
With very large teeth or with inappropriate volumes, a combination machine can be considered which can carry out both the gear cutting operations and also the preparatory cutting operations such as turning, milling or drilling or further additional operations such as plane and/or external circular grinding.
There are already different concepts for the machining of large teeth which are frequently oriented on the portal construction of large upright machining centers such as disclosed, e.g., by DE 20 2007 012 450.
In the shown upright machining center of the so-called double-column type, the two columns move parallel to the workpiece (Y direction) and thus move the cross-member fastened between these two columns over the workpiece. A support carriage is mounted on the cross-member which can be moved along the transverse carriage at a right angle (X direction) to the direction of travel of the columns. Practically all positions over the workpiece can be traveled to by these movements in the X/Y directions with a sufficient travel path.
The delivery of the cutting tool to the workpiece takes place via a lowering movement of the cross-bar (W direction) and a vertical delivery (Z direction, parallel to the W direction) of the RAM configuration with the milling head fastened thereto to bring the tool into engagement with the workpiece. The cross-bar in this configuration has to absorb bending and torsion forces which result from the machining forces and the weight of the machining head.
A gear-cutting machine in a vertical construction is described in a similar embodiment in DE 10 2009 008 012 A.1 The two columns having the cross-bar are not moved, but are stationary, with respect to the first-named publication. Instead the machine table moves relative to the workpiece in the direction of the machining head. The moved masses of the machine table are smaller in this embodiment with respect to the above-named embodiment.
With large teeth, especially when large modules are milled, very large machining forces arise which nevertheless result in a bending of the cross-bar and of the vertical guide of the ram configuration. These forces in turn have the result of a quality reduction of the gears thus milled independently of whether the gear-cutting process is a hobbing or profile milling process. The assembly arrangement of the gear-cutting milling head at a cross-member with a RAM configuration is considerably inferior to the classical design of a gear-cutting machine in accordance with the prior art with respect to the precision and the force absorption from the gear-cutting milling process. The forces are, however, lower, have a different direction of force effect and can be absorbed more easily by this construction without any great losses in quality for the normal turning, milling or drilling operation carried out at these workpieces. If the second machining is a grinding machining, even lower forces have to be taken up by the second machining head.
Within this arrangement, too, the length of the cross-member has a considerable influence on its bending and torsion properties or a shorter cross-member of the same construction has much better properties with respect to its bending and torsion.
The present disclosure now combines the positive properties of a gear-cutting machine with the positive properties of an upright machining center for turning/milling operations in a two-column embodiment and in so doing simultaneously increases the stability of the total machine. This is achieved by a machine tool having a correspondingly smaller space requirement being required instead of a plurality of individual machines.
From the aspect of the basic design, a gear-cutting machine for large machines in accordance with the prior art is combined with a vertical turning/milling device having two columns. With respect to the prior art, however, this machine differs at least in that the transverse portal does not extend over the total machine width and in this respect has to be very long and thus flexible. In the machine in accordance with the present disclosure, the second column is located in the middle of the machine table, where the self-supporting length can be almost halved and the cross-beam becomes a lot stiffer or can be configured with a smaller cross-section with the same bending stiffness.
To load the workpieces onto the machine table, the cross-member/portal carrier in the machine in accordance with the present disclosure is configured as outwardly pivotable. In addition, the column in the middle of the machine in the table can be lowered so that the workpieces can be conveyed more easily onto the table.
The outward pivotability of the cross-member/portal carrier furthermore offers still a further advantage. Further machining units and/or tool holders can thus be supported within the machine housing at defined preparation spaces. These spaces can be moved to under NC control by the machining head via the portal carrier. A change of the machining heads and/or a tool change can take place there via an automatic interface in dependence on the design of the selected interface or in accordance with the selected machining operation.
In a further embodiment of the portal carrier, it can be lowered together with the middle column and the outer column so that the linear axles of the RAM configuration do not project so far outwardly during machining, which produces a much more stable axle, which in turn produces a better machining result or makes much higher cutting performances possible.
A movability of the transverse portal over the workpiece is not necessary since rotationally symmetrical workpieces may be machined using this machine. All required work positions can be traveled to by a combination of the rotational movement of the table with a linear travelability of the second machining unit radially to the table.
Further details of the present disclosure will be described in the drawing with reference to schematically shown embodiments.